Fan speed control for refrigeration system



y 15, 1 D- J. PETRANEK 3,455,118

' v A. FAN SPEED CONTROL FOR REFRIGERATION SYSTEM Filed Dec. 26, 1967 INVENTOR, DAVID J. PETRANEK ATTORNEY United States Patent 01 3,455,118 FAN SPEED CONTROL FOR REFRIGERATION SYSTEM David J. Petranek, La Crosse, Wis., assignor to The Trane Company, La Crosse, Wis., a corporation of Wisconsin Filed Dec. 26, 1967, Ser. No. 693,442 Int. Cl. Fd 17/04 U.S. Cl. 62-180 8 Claims ABSTRACT OF THE DISCLOSURE Background of the invention This invention relates to air conditioning systems and more specifically to control means therefor.

This invention has particular utility in transport air conditioning systems used in the transportation of goods which must be maintained at controlled temperatures such as frozen foods and produce. Such systems employ refrig eration systems having the usual refrigerant compressor, condenser, and evaporator serially connected. A fan is generally employed to circulate air within the conditioned space and through the evaporator heat exchanger which is arranged in fluid communication with the conditioned space.

Generally, a prime mover such as an internal combustion engine with an electric generator is employed to drive the compressor and fan, and the electrical heaters if used.

Of course, the thermal load on the air conditioning system will vary from time to time depending upon several factors including variations in ambient temperatures. It therefore is necessary to control the capacity of such conditioning systems.

One successful method of control has been to vary the speed of the prime mover. While it is not always practical to continually match the prime mover speed to the air conditioning load, it is practical to use a continuously running prime mover which is operated at several different speeds to obtain capacity control of the refrigeration systern. A two-speed control cycle is most frequently employed. In addition to obtaining a satisfactory capacity control, such systems have the inherent advantage of fewer failures due to starting difiiculties as the prime mover runs continuously while the unit is in use.

The disadvantage that has accompanied refrigeration systems employing speed control has been the existence of substantial temperature variations within the conditioned space. These variations present themselves as hot or cold spots in the conditioned space which can be particularly detrimental in the case of frozen goods that thaw or chilled produce which freezes.

To eliminate this disadvantage, it has been suggested in US. Patent 3,276,220 that a two'speed variable torque reconnected single winding induction motor be used to drive the evaporator fan. When the engine and generator are operated at high speed, the motor would be connected to a certain number of poles. When the engine and generator are operated at low speed, the fan motor is reconnected to present fewer poles and thus operates at a gen- Patented July 15, 1969 erally uniform speed despite the variations in engine speed. The system requires a special motor and substantial switching apparatus for reconnecting the motor.

The instant invention eliminates the need for a special motor and eliminates the reconnecting switch apparatus.

The instant invention thus provides a simpler and more reliable means for maintaining the evaporator fan speed relatively uniform despite variations in the prime mover speed for purposes of varying capacity of the refrigeration system.

The objectives are achieved by the use of a gated semiconductor switch arranged in series with the fan motor triggered to conduct in a manner to maintain the motor speed relatively uniform.

This invention involves an air conditioning system comprising in combination with a conditioned space; a mechanical refrigeration system including a first heat exchanger, a refrigerant throttling means, a second heat exchanger and a refrigerant compressor serially connected in a closed refrigerant circuit; fan means for passing air in heat exchange relation with said first heat exchanger to said conditioned space; an electric motor for driving said fan means; a prime mover; means for drivingly connecting said prime mover to said electric motor and said compressor; said last named means including an electric alternating current generator; means for varying the capacity of said compressor by varying the speed of said prime mover between a relatively low first rate and a relatively high second rate; a gated semiconductor switch; circuit means serially connecting said motor, said switch, and said generator; circuit means connected to the gate of said switch for triggering said switch to a conducting state at an angular position in the frequency cycle; and means for varying said angular position between a relatively small angle upon operation of said prime mover at said relatively low first rate and a relatively large angle upon operation of said prime mover at said relatively high second rate.

Other objects and advantages will become apparent as this specification proceeds to describe the invention in detail with reference to the accompanying drawing in which the sole figure is a schematic of an air conditioning system embodying the instant invention.

Now referring to the drawing it will be seen that an air conditioned space 10, which may be the cargo space of a railway refrigeration car or refrigeration truck, is provided with a refrigeration system generally designated by numeral 12. While refrigeration system 12 may be of the reversible heat pump type, for purposes of illustrating the invention it has been shown as for cooling only. The refrigeration system includes a refrigerant compressor 14, a refrigerant condenser 16, a refrigerant throttling means such as for example temperature responsive expansion valve 18, and evaporator 20 serially connected in a closed refrigerant loop.

The refrigeration system 12 is powered by an internal combustion engine 22 having a fuel control such as carburetor 24 which operates engine 22 at low speed when solenoid 26 is de-energized and high speed when solenoid 26 is energized.

Engine 22 is drivingly connected to compressor 14. A fan 28 for passing cooling air over condenser 16 is shown as also being driven by engine 22. Engine 22 is also drivingly connected to an alternating current generator 30. It will be appreciated that egine 22 and thus generator 30, compressor 14 and condenser fan 28 operate at a relatively low rate when solenoid 26 is de-energized and at a relatively higher rate when solenoid 26 is energized Evaporator fan 32 is arranged to circulate the air of the conditioned space 10 over evaporator coil 20 for purposes of uniformly cooling space 10. Fan 32 is driven by alternating current electric motor 34. The power circuit for motor 34 includes generator 30, a symmetrical gated semiconductor switch 36, and motor 34 serially connected. The operation of switch 36 will be explained subsequently in connection with the operation of the invention.

An engine control circuit includes generator 30, solenoid 26, and thermostatic switch 38 connected in series. Switch 38 is actuated by bellows 40 which is connected to a temperature sensing bulb 42 disposed to sense the temperature of the conditioned space.

For purposes of controlling symmetrical gated switch 36 an RC circuit is arranged in parallel relation to switch 36 and includes capacitor 44 and resistor 46. A bi-directional diode 48 connects the gate of switch 36 to a point in the RC circuit between capacitor 44 and resistor 46. A switch 50 is disposed in parallel relationship with resistor 46. Switch 50 is operated by bellows 40 so as to be open when switch 38 is closed and to be closed when switch 38 is open.

Operation It is assumed that engine 22, generator 30, compressor 14, and fan 28 are operating. Refrigerant is compressed by compressor 14 and delivered to condenser 16 where the cooling air circulated over the condenser 16 by fan 28 condenser condenses the refrigerant gas to a liquid. The liquid refrigerant then flows to expansion valve 18 where it is throttled to a lower pressure into evaporator 20. Heat absorbed from the conditioned space evaporates the refrigerant which is then returned to compressor 14 for recirculation. The operation of the refrigerant circuit whether operated at high or low speed is similar eXcept that at high speed the refrigerant circulates at a higher rate and a greater quantity of heat is absorbed at the evaporator 20 and rejected at the condenser 16.

For purposes of describing the control circuits for solenoid 26 and symmetrical gated switch 36, let it be assumed that the temperature of space 10 is above the predetermined value at which the pressure in bulb 42 and bellows actuator 40 close switch 38 and open switch 50. A circuit is completed from generator 30, through switch 38 and solenoid 26 thereby energizing solenoid 26 to position carburator 24 to a high speed position causing engine 22, generator 30, compressor 14 and fan 28 all to operate at a relatively high rate.

A second circuit is completed from generator 30, through motor 34 and the RC circuit of resistor 46 and capacitor 44. It should be understood that because of the values selected for capacitor 44 and resistor 46, the current in this circuit is small and is per se below the valve required to operate fan motor 34. During each half cycle the current passing in the RC circuit charges capacitor 44 to a predetermined voltage at which value bi-directional diode 48 conducts to trigger symmetrical gated switch 36. Once triggered switch 36 conducts for the remainder of the half cycle. Resistor 46 serves to limit the charging rate of capacitor 44 and thus causes switch 36 to be triggered to conduct at a relatively large angular position thereby limiting the current to fan motor 34.

Now assume that by operation of the refrigeration system, space 10 is cooled down to a second predetermined lower temperature at which value bulb 42 and bellows 40 actuates switch 38 to the open position and switch 50 to the closed position. Switches 38 and 50 should be designed so their actuation occurs simultaneously. Opening of switch 38 de-energizes solenoid 26 to cause engine 22 and thus generator 30, compressor 14, and fan 28 to be operated at a reduced rate thereby reducing the cooling capacity of the refrigeration system 12. The voltage and frequency of generator 30 is accordingly reduced. Except for the instant invention motor 34 would also operate at a lower rate thus permitting warm and cold spots to occur in the conditioned space.

However, closure of switch 50 shunts out resistor 46 whereby capacitor is changed at a faster rate. Since capacitor 44 is changed at a faster rate, the voltage at which bi-directional diode conducts is reached at a smaller angular position of the voltage cycle thereby causing switch 36 to be triggered to a conducting condition at a smaller angular position of the voltage cycle. Despite the fact that the output voltage and frequency of generator 30 are lower, switch 36 now operates to conduct a greater period of time thereby operating motor 34 at about the same speed as when the refrigeration system is operated at high speed. Fan 32 thus continues to operate at a uniform speed despite the speed variations of engine 22 thereby preventing warm and cold spots from occurring in the conditioned space 10.

While a two speed scheme of operation has been disclosed for illustrating the invention it should be appreciated that an infinitely modulated type control may be used. In this case switches 50 and 36 may be replaced by variable potentiometers and arranged so that as the throttle at carburator 24 is opened, the resistance of the potentiometer replacing switch 50 is reduced.

I claim:

1. An air conditioning system comprising in combination with a conditioned space; a mechanical refrigeration system including a first heat exchanger, a refrigerant throttling means, a second heat exchanger, and a refrigerant compressor serially connected in a closed refrigerant circuit; fan means for passing air in heat exchange relation with said first heat exchanger to said conditioned space; an electric motor for driving said fan means; a prime mover; means for drivingly connecting said prime mover to said electric motor and said compressor; said last named means including an electric alternating current generator; means for varying the capacity of said compressor by varying the speed of said prime mover between a relatively low first rate and a relatively high second rate; a gated semiconductor switch; circuit means serially connecting said motor, said switch, and said generator; circuit means connected to the gate of said switch for triggering said switch to a conducting state at an angular position in the frequency cycle; and means for varying said angular position between a relatively small angle upon operation of said prime mover at said relatively low first rate and a relatively large angle upon operation of said prime mover at said relatively high second rate.

2. The apparatus as defined by claim 1 wherein said gated semiconductor switch is a symmetrical gated switch and said circuit means connected to the gate of said switch includes a bi-directional diode switch in series with the gate of said symmetrical gated switch.

3. An air conditioning system comprising in combination with a conditioned space; an air conditioning apparatus disposed in heat exchange relationship with said space; fan means for circulating air in the conditioned space; an electric motor drivingly connected to said fan means; a generator means for generating an alternating current; a prime mover for providing power to said air conditioning apparatus and said generator; means responsive to the temperature of the conditioned space for varying the speed of said prime mover between a relatively low first rate and a relatively high second rate for varying the capacity of said air conditioning systems; a gated semiconductor switch; circuit means serially connecting said motor, said switch, and said generator means; circuit means connected to the gate of said switch for triggering said switch to a conducting state at an angular position in the frequency cycle; and means for varying said angular position between a relatively small angle upon operation of said prime mover at said relatively low first rate and a relatively large angle upon operation of said prime mover at said relatively high second rate.

4. The apparatus as defined by claim 3 wherein said gated semiconductor switch is a symmetrical gated switch and said circuit means connected to the gate of said switch includes a bi-directional diode switch in series with the gate of said symmetrical gated switch.

5. Apparatus for use in a refrigeration system com prising in combination: a generator means for generating an alternating current; an electrical load; means for varying the output frequency of said generator means between a relatively low rate and a relatively high rate; a gated semiconductor switch; circuit means serially connecting said load, said switch, and said generator means; circuit means connected to the gate of said switch for triggering said switch to a conducting state at an angular position in the frequency cycle; and means for varying said angular position between a relatively small angle upon operation of said generator means at said relatively low freqency rate and a relatively large angle upon operation of said generator means at said relatively high frequency rate.

6. The apparatus as defined by claim 5 wherein said gated semiconductor switch is a symmetrical gated switch and said circuit means connected to the gate of said switch includes a bi-directional diode switch in series with the gate of said symmetrical gated switch.

7. Apparatus for use in a refrigeration system comprising a prime mover, a generator means for generating an alternating current, means drivingly connecting said prime mover to said generator means; an electric motor; means for varying the speed of said prime mover between a relatively low first rate and a relatively high second rate; a gated semiconductor switch; circuit means serially connecting said motor, said switch, and said generator means; circuit means connected to the gate of said switch for triggering said switch to a conducting state at an angular position in the frequency cycle; and means for varying said angular position between a relatively small angle upon operation of said prime mover at said relatively low first rate and a relatively large angle upon operation of said prime mover at said relatively high second rate.

8. The apparatus as defined by claim 7 wherein said gated semiconductor switch is a symmetrical gated switch and said circuit means connected to the gate of said switch includes a bi-directional diode switch in series with the gate of said symmetrical gated switch.

References Cited UNITED STATES PATENTS 2,962,873 12/1960 Anderson 62-l80 3,324,372 6/1967 Myers 318-345 XR 3,390,539 7/1968 Miner 62180 XR 3,403,314 9/1968 Maynard 3l8-345 XR MEYER PERLIN, Primary Examiner US. Cl. X.R, 62226, 229, 323; 318-345 

